Both hypertensive and atherosclerotic vascular disease can be conceptualized as dysregulated or maladaptive remodeling of the vascular wall in response to alterations in the humoral (e.g., growth factor, cytokine) and biomechanical (e.g., hemodynamic) milieu. There is increasing evidence to support an important role for TGF-beta and related growth factors in the pathogenesis of these disorders however, the cellular and molecular mechanisms responsible for the actions of these growth factors in the vessel wall are largely unknown. Smad proteins are a recently identified class of intracellular signaling molecules that are essential components of the signaling pathways utilized by the TGF-beta superfamily of growth factors. Recent work has identified novel members of this family expressed in human vascular endothelium that can modulate gene expression in response to both humoral (i.e., TGF-beta) and biomechanical (i.e., shear stress) stimulation. In this application we propose to use a series of in vitro molecular biological approaches including a Smad protein-dependent transcriptional assay and a mammalian two hybrid system to demonstrate that Smad proteins are part of a novel signaling pathway mediating both growth factor and biomechanical (flow) responses in endothelial cells. To investigate the roles of these pathways in vivo, we will utilize targeted overexpression of a well characterized inhibitory Smad protein (Smad7) to selectively modulate Smad-protein signaling pathways in vascular endothelium or vascular smooth muscle in vivo. Transgenic lines of mice expressing Smad7 via either the TIE-2 promoter or the SM22alpha promoter will be generated and used to examine the role of Smad protein-dependent signaling pathways in the process of vascular remodeling. In addition, these mice will be crossed into the atherosclerosis-susceptible strain of mice (LDL receptor null) to examine the role of these pathways in the pathogenesis of atherosclerosis. By elucidating the roles of these novel signaling molecules in vascular homeostasis and disease pathogenesis, these studies should provide fundamental insights into vascular cell signaling mechanisms and the role of TGF-beta and related growth factors in the vessel wall. These insights may reveal targets for future diagnostic and therapeutic interventions in vascular disease.